U.S. patent application number 10/333834 was filed with the patent office on 2003-08-28 for discharge lamp igniter device and projector device.
Invention is credited to Suzuki, Toshio.
Application Number | 20030160576 10/333834 |
Document ID | / |
Family ID | 19015964 |
Filed Date | 2003-08-28 |
United States Patent
Application |
20030160576 |
Kind Code |
A1 |
Suzuki, Toshio |
August 28, 2003 |
Discharge lamp igniter device and projector device
Abstract
A discharge lamp lighting device for lighting a discharge lamp
(1) comprises: an ignitor (2) as starting means for applying a
starting voltage to the discharge lamp (1) at the time of starting
and thus lighting the discharge lamp (1); a voltage detection
circuit (3) for detecting a voltage of the discharge lamp (1); and
a current control circuit section (5) for controlling a current
supplied to the discharge lamp (1) on the basis of the result of
detection at the voltage detection circuit (3); wherein the current
control circuit section (5), after ignition, starts controlling the
current supplied to the discharge lamp (1) on the basis of the
result of detection at the voltage detection circuit (3) and
continuously increases the current supplied to the discharge lamp
(1) at a predetermined rate of increase. Thus, a discharge lamp
lighting device which is inexpensive and highly reliable and
enables a longer lifetime of the discharge lamp (1) is
provided.
Inventors: |
Suzuki, Toshio; (Kanagawa,
JP) |
Correspondence
Address: |
Jay H Maioli
Cooper & Dunham
1185 Avenue of The Americas
New York
NY
10036
US
|
Family ID: |
19015964 |
Appl. No.: |
10/333834 |
Filed: |
April 28, 2003 |
PCT Filed: |
June 10, 2002 |
PCT NO: |
PCT/JP02/05746 |
Current U.S.
Class: |
315/291 ;
315/224 |
Current CPC
Class: |
Y02B 20/00 20130101;
H05B 41/2882 20130101; H05B 41/388 20130101; H05B 41/2928 20130101;
Y02B 20/208 20130101 |
Class at
Publication: |
315/291 ;
315/224 |
International
Class: |
H05B 037/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 8, 2001 |
JP |
2001-174720 |
Claims
1. A discharge lamp lighting device for lighting a discharge lamp
comprises: starting means for applying a starting voltage to said
discharge lamp at the time of starting and thus lighting said
discharge lamp; voltage detection means for detecting a voltage of
said discharge lamp; and current control means for controlling a
current supplied to said discharge lamp on the basis of the result
of detection at said voltage detection means; wherein said current
control means, after ignition, starts controlling the current
supplied to said discharge lamp on the basis of the result of
detection at said voltage detection means and continuously
increases the current supplied to said discharge lamp at a
predetermined rate of increase to a predetermined current value
larger than a steady-state current of said discharge lamp.
2. The discharge lamp lighting device as claimed in claim 1,
wherein said current control means has voltage correction setting
means for correcting the result of detection from said voltage
detection means, and controls the current supplied to said
discharge lamp on the basis of the detected voltage corrected by
the voltage correction setting means, and the voltage correction
setting means performs correction to continuously decrease the
detected voltage after said ignition at a predetermined rate of
decrease from a predetermined voltage value, thus continuously
changing the current supplied to said discharge lamp at a
predetermined rate of increase.
3. The discharge lamp lighting device as claimed in claim 1,
wherein said current control means has power setting control means
for controlling a target power value of power setting means which
controls the current supplied to said discharge lamp, and the power
setting control means performs control to continuously increase the
target power value after said ignition at a predetermined rate of
increase, thus continuously changing the current supplied to said
discharge lamp at a predetermined rate of increase.
4. A projector device comprising: a discharge lamp; a discharge
lamp lighting device for lighting said discharge lamp; and an
optical system for projecting light emitted from said discharge
lamp to outside; said discharge lamp lighting device comprising:
starting means for applying a starting voltage to said discharge
lamp at the time of starting and thus lighting said discharge lamp;
voltage detection means for detecting a voltage of said discharge
lamp; and current control means for controlling a current supplied
to said discharge lamp on the basis of the result of detection at
said voltage detection means; wherein said current control means,
after ignition, starts controlling the current supplied to said
discharge lamp on the basis of the result of detection at said
voltage detection means and continuously increases the current
supplied to said discharge lamp at a predetermined rate of increase
to a predetermined current value larger than a steady-state current
of said discharge lamp.
5. The projector device as claimed in claim 4, wherein said optical
system has means for modulating and emitting light emitted from
said discharge lamp on the basis of an inputted image signal.
6. The projector device as claimed in claim 4, wherein said current
control means has voltage correction setting means for correcting
the result of detection from said voltage detection means, and
controls the current supplied to said discharge lamp on the basis
of the detected voltage corrected by the voltage correction setting
means, and the voltage correction setting means performs correction
to continuously decrease the detected voltage after said ignition
at a predetermined rate of decrease from a predetermined voltage
value, thus continuously changing the current supplied to said
discharge lamp at a predetermined rate of increase.
7. The projector device as claimed in claim 4, wherein said current
control means has power setting control means for controlling a
target power value of power setting means which controls the
current supplied to said discharge lamp, and the power setting
control means performs control to continuously increase the target
power value after said ignition at a predetermined rate of
increase, thus continuously changing the current supplied to said
discharge lamp at a predetermined rate of increase.
Description
TECHNICAL FIELD
[0001] This invention relates to a discharge lamp lighting device
for lighting a discharge lamp, and a projector device.
BACKGROUND ART
[0002] Discharge lamps are currently used in various fields, for
example, as a light source of an LCD projector device or the like.
In a conventional current control method at the time of lighting
such a discharge lamp, immediately after ignition when a lamp
lighting switch is turned on, the current is fixed at a magnitude
approximately 1.5 to 2 times the magnitude of the steady-state
current of the discharge lamp, and after the lapse of a
predetermined time, that is, when the discharge state of the
discharge lamp is stabilized and the voltage of the discharge lamp
is raised to a predetermined level, the current is reduced and the
steady-state current is gradually restored.
[0003] However, in the current control method as described above,
since a large current which is greater than the steady-state
current flows through the discharge lamp every time the discharge
lamp is lit, the electrodes of the discharge lamp are quickly
exhausted, shortening the lifetime of the discharge lamp.
[0004] To prevent the shortening of the lifetime of the discharge
lamp, the electrodes of the discharge lamp must be less exhausted.
For this, the preset value at which the current is fixed after
ignition may be lowered.
[0005] However, the larger quantity of current is supplied to the
discharge lamp, the faster the discharge state of the discharge
lamp is stabilized. Therefore, if the preset value at which the
current is fixed after ignition is lowered, the rise in voltage of
the discharge lamp becomes too slow and it takes long to stabilize
the discharge lamp.
[0006] It may be considered to dividedly control the current on
several stages after ignition. In this case, however, the current
control circuit is complicated, increasing the cost of discharge
lamp lighting device rises and lowering its reliability.
[0007] Thus, a discharge lamp lighting device which is inexpensive
and highly reliable and enables a longer lifetime of a discharge
lamp has not been realized yet.
DISCLOSURE OF THE INVENTION
[0008] In view of the foregoing status of the art, it is an object
of the present invention to provide a discharge lamp lighting
device which is inexpensive and highly reliable and enables a
longer lifetime of a discharge lamp, and a projector device.
[0009] In order to achieve the above-described object, a discharge
lamp lighting device for lighting a discharge lamp according to the
present invention comprises: starting means for applying a starting
voltage to the discharge lamp at the time of starting and thus
lighting the discharge lamp; voltage detection means for detecting
a voltage of the discharge lamp; and current control means for
controlling a current supplied to the discharge lamp on the basis
of the result of detection at the voltage detection means; wherein
the current control means, after ignition, starts controlling the
current supplied to the discharge lamp on the basis of the result
of detection at the voltage detection means and continuously
increases the current supplied to the discharge lamp at a
predetermined rate of increase to a predetermined current value
larger than a steady-state current of the discharge lamp.
[0010] The discharge lamp lighting device according to the present
invention constituted as described above has the current control
means for controlling a current supplied to the discharge lamp on
the basis of the result of detection at the voltage detection
means, and this control means performs control to continuously
change the quantity of current supplied to the discharge lamp after
ignition at a predetermined rate of increase to a predetermined
current value larger than a steady-state current of the discharge
lamp on the basis of the result of detection of the voltage of the
discharge lamp.
[0011] That is, in this discharge lamp lighting device, after
ignition when lighting the discharge lamp, the quantity of current
is continuously changed at a predetermined rate of increase to a
predetermined current value larger than a steady-state current of
the discharge lamp and the current is thus supplied to the
discharge lamp.
[0012] To this end, voltage correction setting means for correcting
the result of detection from the voltage detection means is
provided in the current control means so that the current supplied
to the discharge lamp is controlled on the basis of the detected
voltage corrected by this voltage correction setting means. This
voltage correction setting means performs correction to
continuously decrease the detected voltage after the ignition at a
predetermined rate of decrease from a predetermined voltage value,
thus enabling continuous change in the current supplied to the
discharge lamp at a predetermined rate of increase.
[0013] Moreover, power setting control means for controlling a
target power value of power setting means which controls the
current supplied to the discharge lamp is provided in the current
control means. This power setting control means performs control to
continuously increase the target power value after the ignition at
a predetermined rate of increase, thus enabling continuous change
in the current supplied to the discharge lamp at a predetermined
rate of increase.
[0014] In this discharge lamp lighting device, by thus controlling
the quantity of current, the time during which a large current
larger than the steady-state current flows through the discharge
lamp is significantly reduced, compared with the conventional
discharge lamp lighting device.
[0015] Moreover, in this discharge lamp lighting device, by thus
controlling the quantity of current, the current supplied to the
discharge lamp is gradually increased and therefore the electrodes
of the discharge lamp are gradually warmed up. As a result, heat
load on the electrodes is reduced and thermal fatigue of the
electrodes is reduced, thus restraining the exhaustion of the
electrodes.
[0016] Furthermore, a projector device which projects light emitted
from a discharge lamp to outside can be constituted by using the
discharge lamp lighting device as described above. This projector
device may be a projector device which modulates light emitted from
the discharge lamp on the basis of an inputted image signal and
emits the modulated light.
[0017] Also in the case of the projector device, similar to the
discharge lamp lighting device, since the time during which a large
current larger than the steady-state current flows through the
discharge lamp is significantly reduced and the current supplied to
the discharge lamp is gradually increased, the electrodes of the
discharge lamp are gradually warmed up. Therefore, heat load on the
electrodes is reduced and thermal fatigue of the electrodes is
reduced, thus restraining the exhaustion of the electrodes.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a block diagram showing the schematic structure of
an embodiment of a discharge lamp lighting device to which the
present invention is applied.
[0019] FIG. 2 is a schematic sectional view showing an exemplary
structure of a discharge lamp.
[0020] FIG. 3 is a graph showing the state of current and voltage
in a conventional discharge lamp lighting device.
[0021] FIG. 4 is a graph showing the state of current and voltage
in the embodiment of the discharge lamp lighting device according
to the present invention.
[0022] FIG. 5 is a structural view showing an exemplary structure
of a control circuit.
[0023] FIG. 6 shows the transition of an input V.sub.i to a control
circuit 6 and an output V.sub.o from the control circuit 6.
[0024] FIG. 7 is a block diagram showing an exemplary structure of
the embodiment of the discharge lamp lighting device to which the
present invention is applied.
[0025] FIG. 8 is a block circuit diagram showing an exemplary
circuit structure of an essential part in the case of performing
control to gradually increase a current after turning on a lamp
lighting switch by a voltage correction setting circuit of FIG.
7.
[0026] FIG. 9 shows waveforms for explaining the operation of the
circuit of FIG. 8.
[0027] FIG. 10 is a block circuit diagram showing an exemplary
circuit structure of an essential part in the case of performing
control to gradually increase a current after turning on the lamp
lighting switch by a power setting control circuit of FIG. 7.
[0028] FIG. 11 shows waveforms for explaining the operation of the
circuit of FIG. 10.
[0029] FIG. 12 is a block diagram showing the schematic structure
of a projector device using a discharge lamp, as an embodiment of
the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
[0030] The best mode for carrying out the invention will now be
described with reference to the drawings.
[0031] FIG. 1 is a block diagram showing the schematic structure of
an embodiment of a discharge lamp lighting device to which the
present invention is applied.
[0032] The discharge lamp lighting device to which the present
invention is applied has an ignitor 2 as starting means for
applying a starting voltage to a discharge lamp 1 at the time of
starting and thus lighting the discharge lamp 1, a voltage
detection circuit 3 as voltage detection means for detecting a
voltage applied to the discharge lamp 1, a current detection
circuit 4 as current detection means for detecting a current
flowing through the discharge lamp 1, and a current control circuit
section 5 as current control means for controlling the current
flowing through the discharge lamp 1 (or controlling power supplied
to the discharge lamp 1) on the basis of the result of detection at
the voltage detection means, as shown in FIG. 1. The current
control circuit section 5 is constituted by connecting a control
circuit 6, a PWM controller 7 and a down converter 8 in this
order.
[0033] The input terminal of the down converter 8 is connected with
a DC power source 9, as shown in FIG. 1, so that a current is
supplied to the discharge lamp lighting device. As the DC power
source 9, for example, a power source which outputs a voltage of
approximately 300 to 400 V with an active filter or the like may be
used.
[0034] The output terminal of the down converter 8 is connected
with the input terminal of the ignitor 2, so that the direct
current supplied from the DC power source 9 is controlled and
converted to an appropriate magnitude through the down converter 8
and then supplied to the ignitor 2.
[0035] The output terminal of the ignitor 2 is connected with the
input terminal of the discharge lamp 1, so that the direct current
flowing from the down converter 8 to the ignitor 2 is supplied
directly to the discharge lamp 1.
[0036] The discharge lamp 1 has a connector 11, a reflector 12,
electrodes 13, and a heat-resistant glass 14 covering the
electrodes 13, as shown in FIG. 2. An ignition voltage, a lamp
current and the like are supplied from the connector 11 to the
electrodes 13. Various gases are sealed within the heat-resistant
glass 14 and the electrodes 13 discharge within the heat-resistant
glass 14.
[0037] The discharge lamp to which the discharge lamp lighting
device according to the present invention can be applied is not
particularly limited. Any discharge lamp in which a voltage changes
before stabilization, for example, a metal halide lamp, a
high-pressure mercury lamp, or a xenon lamp, may be used.
[0038] The voltage detection circuit 3 and the current detection
circuit 4 are arranged in a branched manner between the output
terminal of the down converter 8 and the input terminal of the
ignitor 2. The output terminal of the voltage detection circuit 3
and the output terminal of the current detection circuit 4 are
connected to the input terminal of the control circuit 6 in the
current control circuit section 5.
[0039] The current control circuit section 5 is adapted for
controlling a current supplied to the discharge lamp 1 after
ignition. As described above, the current control circuit section 5
is constituted by connecting the control circuit 6, the PWM
controller 7 and the down converter 8 in this order. The control
circuit 6 starts controlling the current supplied to the discharge
lamp 1 on the basis of the result of detection at the voltage
detection means, and controls the current on the basis of the
result of detection at the voltage detection circuit 3 so as to
realize an appropriate quantity of current supplied to the
discharge lamp 1.
[0040] In this discharge lamp lighting device, the current supplied
to the discharge lamp 1 is controlled by controlling the voltage
applied to the discharge lamp 1. That is, in this discharge lamp
lighting device, the voltage applied to the discharge lamp 1 is
changed and controlled, thereby controlling the quantity of current
supplied to the discharge lamp 1.
[0041] Specifically, the current control circuit section 5 is
adapted for controlling the power supplied to the discharge lamp 1
at a predetermined constant value. The operation of the down
converter 8 is controlled so that a value (detected power value)
obtained by multiplying the detected voltage at the voltage
detection circuit 3 by the detected current at the current
detection circuit 4 is a predetermined target power value. However,
the resistance value of the discharge lamp 1 immediately after
ignition is very low and the detected voltage value is lowered,
thus excessively increasing the current value for supplying the
predetermined power. Therefore, by correcting the detected voltage
or controlling the target power setting value, the current
immediately after ignition is limited to, for example, a magnitude
approximately 1.5 to 2 times the magnitude of the steady-state
current.
[0042] In the conventional discharge lamp lighting device, control
is performed so that the magnitude of a current supplied to the
discharge lamp (lamp current "a" indicated by a solid line in FIG.
3) is fixed at a magnitude approximately 1.5 to 2 times the
magnitude of a steady-state current in the steady state of the
discharge lamp, immediately after ignition (time point t.sub.ig)
when lighting the discharge lamp, and thus the supply of the
current to the discharge lamp is continued, as shown in FIG. 3.
When the discharge state of the discharge lamp is stabilized after
the lapse of a predetermined time and the voltage of the discharge
lamp (lamp voltage "b" indicated by a broken line in FIG. 3) is
raised to a predetermined level, the current supplied to the
discharge lamp is reduced and the steady-state current is gradually
restored.
[0043] In such a current control method, however, since a large
current which is larger than the steady-state current flows through
the discharge lamp every time the discharge lamp is lit, the time
during which an excessively large current flows through the
discharge lamp becomes longer. Therefore, the electrodes of the
discharge lamp are quickly exhausted, shortening the lifetime of
the discharge lamp.
[0044] To prevent the shortening of the lifetime of the discharge
lamp, the electrodes of the discharge lamp must be less exhausted.
For this, the preset value at which the current is fixed after
ignition may be lowered.
[0045] However, the more power is supplied to the discharge lamp,
the faster the discharge state of the discharge lamp is stabilized.
Therefore, if the preset value at which the current is fixed after
ignition is lowered, the rise in voltage of the discharge lamp
becomes too slow and it takes long to stabilize the discharge
lamp.
[0046] It may be considered to dividedly control the current on
several stages after ignition. In this case, however, the current
control circuit is complicated, increasing the cost of discharge
lamp lighting device rises and lowering its reliability.
[0047] In order to overcome such inconvenience, in this discharge
lamp lighting device, control is performed so that the discharge
lamp 1 is stabilized in a time equivalent to the time required in
the conventional discharge lamp lighting device and the time during
which a large current flows through the discharge lamp 1 is
reduced.
[0048] Specifically, at the current control circuit section 5 in
this discharge lamp lighting device, the quantity of current (lamp
current "a" indicated by a solid line in FIG. 4) supplied to the is
continuously changed at a predetermined rate of increase after
ignition (time point t.sub.ig), as shown in FIG. 4.
[0049] When the quantity of current supplied to the discharge lamp
1 reaches a predetermined value (hereinafter referred to as maximum
current value) which is larger than the steady-state current of the
discharge lamp 1, that is, when the discharge state of the
discharge lamp 1 is stabilized and the voltage (lamp voltage "b"
indicated by a broken line in FIG. 4) of the discharge lamp 1 is
raised to a predetermined level, the quantity of current is
decreased at a predetermined rate of decrease to the steady-state
current of the discharge lamp 1 and then maintained at this
level.
[0050] In this discharge lamp lighting device, by thus controlling
the quantity of current, the time during which a large current
larger than the steady-state current flows through the discharge
lamp 1 can be significantly reduced, compared with the conventional
discharge lamp lighting device.
[0051] Moreover, in this discharge lamp lighting device, by thus
controlling the quantity of current, the current supplied to the
discharge lamp 1 is gradually increased and therefore the
electrodes 13 of the discharge lamp 1 are gradually warmed up. As a
result, heat load on the electrodes 13 can reduced and thermal
fatigue of the electrodes 13 can reduced, thus restraining the
exhaustion of the electrodes 13. Therefore, in this discharge lamp
lighting device, the shortening of the lifetime of the discharge
lamp 1 due to the exhaustion of the electrodes 13 can be prevented
and the discharge lamp 1 with a longer lifetime can be
realized.
[0052] The maximum current value and the rate of increase in
current are not particularly limited and may be properly set in
accordance with various conditions such as the type of the
discharge lamp 1.
[0053] Compared with the conventional discharge lamp lighting
device in which a predetermined large current is caused to flow for
a predetermined time after ignition, the time required for
stabilizing the discharge state of the discharge lamp 1 is only
several seconds at most, though depending on various conditions
such as the type of the discharge lamp 1, the maximum current value
and the rate of increase in current. This causes no problem in
practical application of the discharge lamp 1.
[0054] That is, in this discharge lamp lighting device, the
discharge lamp 1 can be stabilized in a time equivalent to the time
required in the conventional discharge lamp lighting device.
[0055] As the maximum current value is reached, the maximum current
value may be maintained for a predetermined time and then the
quantity of current may be decreased. Alternatively, the quantity
of current may be decreased when the maximum current level is
reached. This, too, may be properly set in accordance with various
conditions such as the type of the discharge lamp 1, correlatively
with the rate of increase in current.
[0056] The control circuit 6 of the current control circuit section
5 may have, for example, a structure made up mainly of a circuit as
shown in FIG. 5.
[0057] The circuit shown in FIG. 5 is an essential part of the
control circuit 6. An input V.sub.i to this circuit shown in FIG. 5
is a voltage based on the result of detection at the voltage
detection circuit 3, as will be described later. When this input
voltage V.sub.i is gradually raised from 0 to an output voltage
V.sub.B of the DC power source 9, an output V.sub.o from the
circuit shown in FIG. 5 can be limited to a value "V.sub.k+V.sub.F"
obtained by adding a divided voltage V.sub.k
(V.sub.k=V.sub.B.times.R.sub.2/(R.sub.1+R.sub.2)) divided from the
power-supply voltage V.sub.B by resistors R.sub.1 and R.sub.2, to a
forward voltage drop V.sub.F of a diode D.sub.1. The output V.sub.o
is a voltage for controlling the voltage supplied to the discharge
lamp 1 or for setting the power supplied to the discharge lamp 1.
More specifically, the circuit of FIG. 5 is equivalent to a power
setting control circuit 60, which will be described later with
reference to FIGS. 7, 10 and 11.
[0058] The values of the resistors R.sub.1 and R.sub.2 can be
freely set and changed. Therefore, in the circuit shown in FIG. 5,
when the input V.sub.i to the circuit, that is, the result of
detection at the voltage detection circuit 3, is gradually raised
from 0 to the output voltage V.sub.B of the DC power source 9, the
output Vo, that is, the voltage corresponding to the voltage
supplied to the discharge lamp 1, can be controlled to be at a
desired value "V.sub.k+V.sub.F" by setting the values of the
resistors R.sub.1 and R.sub.2 at predetermined values which satisfy
the conditions of R.sub.1<R.sub.0 and R.sub.2<R.sub.0 with
respect to a resistor R.sub.0, as shown in FIG. 6. Therefore, the
upper limit of the output Vo, that is, the voltage corresponding to
the voltage applied to the discharge lamp 1, can be controlled.
[0059] Since the current supplied to the discharge lamp 1 can be
controlled by controlling the voltage applied to the discharge lamp
1 as described above, the upper limit of the current supplied to
the discharge lamp 1 can be controlled by controlling the upper
limit of the voltage applied to the discharge lamp 1.
[0060] By changing the values of the resistor R.sub.0 and a
capacitor C.sub.0, the rate of increase in output V.sub.o from the
circuit shown in FIG. 5, of the control circuit 6, can be set at a
predetermined rate of increase. Therefore, the rate of increase in
the current supplied to the discharge lamp 1 can be controlled to
be a desired rate of increase by controlling the rate of increase
in the voltage applied to the discharge lamp 1.
[0061] Moreover, since the essential structure of the control
circuit 6 can be constituted by a simple circuit as shown in FIG.
5, this discharge lamp lighting device has high reliability and can
be produced inexpensively.
[0062] The output V.sub.o controlled at the control circuit 6 as
described above is inputted to the PWM controller 7 and is used as
a control signal for the PWM controller 7. The PWM controller 7
controls the duty factor of ON/OFF operation of a semiconductor
switch provided in the PWM controller 7 in accordance with the
output V.sub.o inputted thereto from the control circuit 6, and
inputs this controlled signal to the down converter 8.
[0063] The down converter 8 controls the current value of the
direct current supplied from the DC power 9 at a predetermined
value on the basis of the signal inputted thereto from the PWM
controller 7, and then outputs the controlled current value.
[0064] Therefore, in this discharge lamp lighting device, a current
controlled to continuously change at a desired rate of increase by
feedback control as described above can be supplied to the
discharge lamp 1.
[0065] The structure shown in FIG. 5 is an example of the essential
structure of the control circuit 6. The control circuit 6 is not
limited to this and various structures having the above-described
function can be used.
[0066] As described above in detail, a discharge lamp lighting
device which has an inexpensive structure and high reliability and
enables a longer lifetime of the discharge lamp 1 can be
realized.
[0067] The operation of the above-described discharge lamp lighting
device will now be described.
[0068] First, ignition is carried out. That is, a predetermined
direct current is supplied from the DC power source 9 to the
ignitor 2 to charge a capacitor in the ignitor 2. When the charging
voltage of the capacitor reaches a predetermined voltage, a high
voltage is generated and applied to the discharge lamp 1. The
application of this high voltage causes dielectric breakdown
between the electrodes 13 of the discharge lamp 1. As a result, the
charging load of the capacitor in the ignitor 2 is discharged
through the discharge lamp 1 and power is continuously supplied to
the discharge lamp 1 to light the discharge lamp 1.
[0069] The lighting of the discharge lamp 1 is detected as a change
in voltage at the voltage detection circuit 3 and this result of
detection is inputted to the control circuit 6 of the current
control circuit section 5.
[0070] After the discharge lamp 1 is lit, the current supplied to
the discharge lamp 1 is detected by the current detection circuit
4. The result of detection at the current detection circuit 4 is
inputted to the control circuit 6 of the current control circuit
section 5.
[0071] Moreover, after the discharge lamp 1 is lit, the voltage
applied to the discharge lamp 1 is detected by the voltage
detection circuit 3. The result of detection at the voltage
detection circuit 3 is inputted to the control circuit of the
current control circuit section 5.
[0072] The control circuit 6 of the current control circuit section
5 starts controlling the current supplied to the discharge lamp 1
after ignition on the basis of the result of detection inputted
thereto from the voltage detection circuit 3, and continuously
changes the current supplied to the discharge lamp 1 at a
predetermined rate of increase.
[0073] When the current value reaches the maximum current value,
that is, when the discharge state of the discharge lamp 1 is
stabilized and the voltage of the discharge lamp 1 is raised to a
predetermined level, the quantity of current is decreased at a
predetermined rate of decrease to the steady-state current of the
discharge lamp 1 and then maintained.
[0074] Then, a control signal controlled at the control circuit 6
as described above is inputted to the PWM controller 7 and is used
as a control signal for the PWM controller 7. The PWM controller 7
controls the duty factor of ON/OFF operation of the semiconductor
switch provided in the PWM controller 7 in accordance with the
output V.sub.0 inputted thereto from the control circuit 6, and
inputs this controlled signal to the down converter 8.
[0075] The down converter 8 controls the current value of the
direct current supplied from the DC power source 9 at a
predetermined value on the basis of the control signal inputted
thereto from the PWM controller 7, and outputs the controlled
current value to the discharge lamp 1 via the ignitor 2. Thus, the
lighting of the discharge lamp 1 is maintained.
[0076] In the discharge lamp lighting device constituted as
described above, the time during which a large current larger than
the steady-state current flows through the discharge lamp can be
significantly reduced, compared with the conventional discharge
lamp lighting device.
[0077] Moreover, heat load on the electrodes and hence heat fatigue
of the electrodes can be reduced, restraining exhaustion of the
electrodes to the minimum level. Therefore, in this discharge lamp
lighting device, shortening of the lifetime of the discharge lamp
due to the exhaustion of the electrodes can be prevented.
[0078] Since the current control means in this discharge lamp
lighting device can be realized with a simple structure, the
discharge lamp lighting device is highly reliable and can be
produced inexpensively.
[0079] Thus, according to the present invention, a discharge lamp
lighting device which is inexpensive and highly reliable and
enables a longer life of the discharge lamp can be provided.
[0080] FIG. 7 is a block diagram showing a more specific exemplary
structure of the discharge lamp lighting device shown in FIG. 1.
The parts shown in FIG. 7 corresponding to the parts shown in FIG.
1 are denoted by the same numerals.
[0081] In FIG. 7, a DC voltage of approximately 300 to 400 V,
specifically, for example, a DC voltage of 370 V, is outputted from
the DC power source 9 constituted by an active filter or the like,
and is fed to the down converter 8. The down converter 8, which is
a step-down switching power source, switches the input DC voltage,
for example, at a frequency of approximately 50 to 100 kHz, and
then smoothes the input DC voltage, thereby carrying out voltage
conversion (voltage drop) to a DC voltage of, for example,
approximately 50 to 100 V, which is necessary for ordinary lighting
of the lamp (discharge lamp). The switching operation of this down
converter 8 is controlled at constant output power as pulse width
control and frequency control are carried out by a control circuit
70 (equivalent to the PWM controller 7 of FIG. 1 or the like).
[0082] The output from the down converter 8 is fed to the ignitor 2
of the ignition section via a full bridge 22. Voltage-division
resistors R.sub.31, R.sub.32 for voltage detection and a resistor
41 for current detection are provided between the down converter 8
and the full bridge 22.
[0083] The ignitor 2 has an ignition output transformer (not
shown). When lighting the lamp, a pulse voltage is supplied to its
primary winding and a pulse signal of approximately 5 to 20 kV is
generated and outputted from its secondary winding (output
winding). The output from this ignitor 2 is supplied to the lamp
(discharge lamp) 1. An ignitor control circuit 21 of FIG. 7 is
adapted for stopping the ignition operation in accordance with
detection of lighting of the lamp by ignition at a lamp ON
detection circuit 23. This example of FIG. 7 represents a circuit
structure for an AC lamp. In the case of a circuit structure for a
DC lamp, the full bridge 22 is not necessary.
[0084] The voltage detection circuit 3 detects voltage-division
outputs from the voltage-division resistors R.sub.31, R.sub.32 and
sends the detected voltage output to a multiplier 42, a power
setting switching circuit 62, and the lamp ON detection circuit 23.
The detection output from the lamp ON detection circuit 23 is sent
to a voltage correction setting circuit 30, the power setting
control circuit 60, and the ignitor control circuit 21. The output
terminal of the voltage correction setting circuit 30 is connected
with the output terminal of the voltage detection circuit 3 via a
diode D.sub.31, so that the higher one of the output
voltage+V.sub.F of the voltage correction setting circuit 30
(forward voltage drop of the diode D.sub.31) and the detected
voltage from the voltage detection circuit 3 is sent to the
multiplier 42 and the power setting switching circuit 62.
[0085] The current detection circuit 4 detects the output current
from the down converter 8 by detecting a voltage generated in the
resistor 41 and then sends the detected output current to the
multiplier 42. The multiplier 42 multiplies the detected voltage
from the voltage detection circuit 3 by the detected current from
the current detection circuit 4, thus calculating the output power
from the down converter 8.
[0086] The outputs from the power setting control circuit 60, the
power setting switching circuit 62 and the multiplier 42 are sent
to the power setting circuit 61. The output from the power setting
circuit 61 is sent as target power to the control circuit 70. As
the control circuit 70 controls the switching operation (pulse
width and the like) of the down converter 8, the output power from
the down converter 8 is ultimately controlled to be the target
power.
[0087] Either the voltage correction setting circuit 30 or the
power setting control circuit 60 of FIG. 7 is controlled to
continuously increase the current supplied to the discharge lamp
after the ignition or after turning on the lamp, at a predetermined
rate of increase to a predetermined current value larger than the
steady-state current of the discharge lamp. Although both the
voltage correction setting circuit 30 and the power setting control
circuit 60 are shown in FIG. 7, at least one of these may be used
and the other may be omitted. More specifically, either a structure
consisting of the voltage correction setting circuit 30 and the
diode D.sub.31 or a structure consisting of the power setting
control circuit 60 and the power setting switching circuit 62 may
be used.
[0088] The multiplier 42, the voltage correction setting circuit
30, the power setting control circuit 60, the power setting circuit
61, the power setting switching circuit 62 and the like, shown in
FIG. 7, are provided within the current control circuit section 5
of FIG. 1 and these can be considered to substantially correspond
to the control circuit 6. The control circuit 70 of FIG. 7
substantially corresponds to the PWM circuit 7 of FIG. 1. However,
the control circuit 70 is not limited to pulse width control and it
controls the output current (or output power) from the down
converter 8 by frequency control or by pulse width and frequency
control.
[0089] A more detailed specific example of the structure of FIG. 7
and an exemplary operation thereof will now be described with
reference to FIGS. 8 to 11.
[0090] First, FIG. 8 is a block diagram showing an exemplary
circuit structure of an essential part in the case where the
voltage correction setting circuit 30 performs control to gradually
increase the current of the discharge lamp at the time of turning
on a lamp lighting switch or after the ignition. FIG. 9 shows
waveforms for explaining the operations shown in FIG. 8. In this
example, a voltage V.sub.1 represents an output voltage from the DC
power source 9 of FIG. 7, and a voltage V.sub.2 and a current
I.sub.1 represent an output voltage and an output current from the
down converter 8 of FIG. 7, respectively. A voltage V.sub.3
represents a voltage detected by the voltage-division resistors
R.sub.31, R.sub.32 and supplied to the multiplier 42 in FIG. 8, and
a voltage V.sub.4 represents an integral output voltage of a
time-constant circuit in the voltage correction setting circuit
30.
[0091] Specifically, in FIG. 8, the connection point between the
voltage-division resistors R.sub.31, R.sub.32 for voltage detection
is connected with the anode of a diode D.sub.2 for clamping and the
cathode of the diode D.sub.31. The cathode of the diode D.sub.2 is
connected with the +Vcc terminal of the circuit power source and
the anode of the diode D.sub.31 is connected with the connection
point between voltage-division resistors R.sub.3, R.sub.4 in the
voltage correction setting circuit 30. Therefore, as the voltage
V.sub.3 at the connection point between the voltage-division
resistors R.sub.3, R.sub.4, one of the voltage-division detection
voltage detected by the voltage-division resistors R.sub.31,
R.sub.32, the anode voltage of the diode D.sub.2, and the cathode
voltage of the diode D.sub.31, is supplied as the ultimate detected
voltage to the multiplier 42. The circuit power-supply voltage +Vcc
is set, for example, at +15 V, but it is not limited to this.
[0092] In the voltage correction setting circuit 30, the
voltage-division resistors R.sub.3, R.sub.4 are inserted and
connected between the +Vcc power-source terminal and an earth
terminal (GND), and a capacitor C.sub.1 is connected in parallel to
the resistor R.sub.3. The capacitor C.sub.1 is connected between
the emitter and the collector of a PNP transistor TR.sub.3, and the
base of the transistor TR.sub.3 is supplied with the output from
the lamp ON detection circuit 23. The output from the lamp ON
detection circuit 23 is 0 V at the time of OFF and +Vcc (for
example, +15 V) at the time of ON. Therefore, when the lamp is off,
the transistor TR.sub.3 is turn on to form a short circuit between
both ends of the capacitor C.sub.1, and after the lamp is turned
on, the transistor TR.sub.3 is turned off and electric charges are
accumulated at the capacitor C.sub.1.
[0093] In such a structure, as the output voltage V.sub.1 from the
DC power source 9 of FIG. 7, a predetermined DC voltage, for
example, 370V, is outputted and supplied to the down converter 8
even before the lamp lighting switch is turned on. As the lamp
lighting switch is turned on at time t.sub.ON in this state, the
ignitor 2 starts the ignition operation as described above and the
resistance value of the discharge lamp 1 is lowered, thus lowering
the voltage supplied to the discharge lamp 1. The lamp ON detection
circuit 23 of FIG. 7 detects this voltage drop and outputs a lamp
ON detection signal, for example, a signal for rise from 0 V to
+Vcc (for example, +15 V). This lamp ON detection signal is sent to
the ignitor control circuit 21 of FIG. 7 and the ignition operation
of the ignitor 2 is stopped. In this case, the output voltage
V.sub.2 from the down converter 8 reaches approximately 300 V in
accordance with the ignition operation and then is normally lowered
to approximately 10 V in a duration Td of approximately 100
microseconds, as shown in FIG. 9. In some cases, the lowering takes
approximately 1 to 3 seconds. Similarly, the output current I.sub.1
from the down converter 8 temporarily rises to approximately 20 A
and then is lowered.
[0094] The lamp ON detection signal from the lamp ON detection
circuit 23 in this case is also sent to the transistor TR.sub.3 of
the voltage correction setting circuit 30 of FIG. 8. As the
transistor TR.sub.3 is turned off and electric charges are
accumulated at the capacitor C.sub.1, the voltage V.sub.4 at the
connection point between the resistors R.sub.3, R.sub.4 in the
voltage correction setting circuit 30 changes as shown in FIG. 9.
In response to this, the ultimate detected voltage V.sub.3 supplied
to the multiplier 42 changes as shown in FIG. 9.
[0095] Specifically, at the time t.sub.ON when the lamp lighting
switch is turned on, the voltage-division output voltage from the
voltage-division resistors R.sub.31, R.sub.32 becomes higher, but
the ultimate detected voltage V.sub.3 is clamped at a predetermined
clamp voltage V.sub.11 by the diode D.sub.2 for clamping. This
clamp voltage is a voltage that is higher than the circuit
power-supply voltage +Vcc (for example, +15 V) by the forward
voltage drop V.sub.F of the diode D.sub.2. That is, this clamp
voltage is expressed as follows.
V.sub.11+Vcc+V.sub.F
[0096] After that, as the transistor TR.sub.3 in the voltage
correction setting circuit 30 is turned off and electric charges
begin to be accumulated at the capacitor C.sub.1, the voltage
V.sub.4 at the connection point between the resistors R.sub.3,
R.sub.4 is gradually lowered on the basis of the time constant
corresponding to the resistance values of the resistors R.sub.3,
R.sub.4 and the capacitance value of the capacitor C.sub.1.
Specifically, the voltage V.sub.4 at the connection point between
the resistors R.sub.3, R.sub.4 changes from the circuit
power-supply voltage +Vcc (for example, +15 V) at the time t.sub.ON
when the lamp lighting switch is turned on, to a divided voltage
V.sub.14 (=+Vcc.times.(R.sub.32/(R.sub.31+R.sub.32)) obtained by
dividing the voltage +Vcc at the resistors R.sub.3, R.sub.4 after a
predetermined time T.sub.AA defined by the time constant. The
voltage V.sub.3 in this case appears as the voltage V.sub.4 passes
through the diode D.sub.31 and therefore it is a voltage that is
lower than the voltage V.sub.4 by the forward voltage drop V.sub.F
of the diode D.sub.31. A voltage V.sub.12 after the lapse of the
predetermined time T.sub.AA is expressed as follows.
V.sub.12=+Vcc.times.(R.sub.32/(R.sub.31+R.sub.32))-V.sub.F
[0097] This voltage V.sub.3 is sent as the ultimate detected
voltage to the multiplier 42 and is multiplied by the detected
current output from the current detection circuit 4 of FIG. 7, thus
becoming target power for power control. Therefore, when the
detected voltage output which is gradually lowered during the time
T.sub.AA is sent to the multiplier 42, the down converter 8 is
controlled so that the output current I.sub.1 is gradually
increased as shown in FIG. 9, via the control circuit 70 from the
power setting circuit 61 of FIG. 7. The output current I.sub.1 is
controlled so that the current supplied to the discharge lamp 1 is
continuously increased to 1.5 times the steady-state current of,
for example, +2 A, that is, it is continuously increased to +3 A.
These current values are only examples and the present invention is
not limited to these numerical values.
[0098] In FIG. 9, a period T.sub.A from the time t.sub.ON when the
lamp lighting switch is turned on to the time t.sub.11 is a lamp
voltage constant period in which the lamp has a low resistance
value. This period has a duration of, for example, approximately 20
to 90 seconds. A period T.sub.B from the time t.sub.11 to the time
12 is a lamp voltage build-up period. The total duration of the
periods T.sub.A and T.sub.B is, for example, approximately 30
seconds to 2 minutes. However, the present invention is not limited
to these numerical values. A period T.sub.C after the time t.sub.12
is a steady-state period in which the discharge state of the lamp
is stable. The output voltage V.sub.2 from the down converter 8 in
the steady state is, for example, +70 V, and the output current
I.sub.1 is +2 A. As a matter of course, the present invention is
not limited to these numerical values. As the voltage detection
output V.sub.3 to the multiplier 42, a voltage V.sub.13 in the
steady-state is voltage detected at the voltage-division resistors
R.sub.31, R.sub.32 for voltage detection. That is, the voltage
V.sub.13 is expressed as follows.
V.sub.13=V.sub.2.times.(R.sub.32/(R.sub.31+R.sub.32))
[0099] According to the specific example described with reference
to FIGS. 8 and 9, the time during which a large current larger than
the steady-state current flows through the discharge lamp can be
reduced, and heat burden on the electrodes and hence thermal
fatigue of the electrodes can be reduced. Therefore, exhaustion of
the electrodes can be restrained to the minimum level and
shortening of the lifetime of the discharge lamp due to the
exhaustion of the electrodes can be prevented.
[0100] FIGS. 10 and 11 explain a specific example of control to
gradually increase the lamp of the discharge lamp after the
ignition by the power setting control circuit 60 of FIG. 7. FIG. 10
is a block circuit diagram showing a specific example of the power
setting control circuit 60 and its peripheral circuit. FIG. 11
shows waveforms for explaining the operation of the circuits of
FIG. 10.
[0101] In FIG. 10, the connection points between the
voltage-division resistors R.sub.31, R.sub.32 for voltage detection
is connected with the anode of the diode D.sub.2 for clamping, and
the cathode of the diode D.sub.2 id connected with the +Vcc
terminal of the circuit power source. In this specific example, the
voltage correction setting circuit 30 is not used. A voltage
V.sub.6 at the connection point between the voltage-division
resistors R.sub.3, R.sub.4 is either a voltage-division detection
voltage detected at the voltage-division resistors R.sub.31,
R.sub.32 or an anode voltage of the diode D.sub.2. This voltage
V.sub.6 is supplied as the ultimate detected voltage to the
multiplier 42 and the power setting switching circuit 62. The
output from the lamp ON detection circuit 23 is supplied as an
input voltage V.sub.i to the power setting control circuit 60.
[0102] The power setting control circuit 60 shown in FIG. 10 is
equivalent to the circuit structure shown in FIG. 5. A resistor
R.sub.9, a capacitor C.sub.2, a diode D.sub.4, and resistors
R.sub.7, R.sub.8 are equivalent to the resistor R.sub.0, the
capacitor C.sub.0, the diode D.sub.1, and the resistors R.sub.1,
R.sub.2 of FIG. 5, respectively. An output voltage V.sub.5 from
this power setting control circuit 60 (V.sub.0 of FIG. 5) is
supplied to the power setting circuit 61.
[0103] As the operation before and after the time t.sub.ON when the
lamp lighting switch is turned on, the output voltage V.sub.2 and
the output current I.sub.1 from the down converter 8 of FIG. 7 are
substantially the same as those described with reference to FIG. 9.
The output V.sub.i from the lamp ON detection circuit 23 is 0 V
when the lamp lighting switch is off before the time t.sub.ON, and
the output V.sub.i is +Vcc (for example, +15 V9 when the lamp
lighting switch is on after the time t.sub.ON. The voltage V.sub.6
at the connection point between the voltage-division resistors
R.sub.3, R.sub.4 is clamped at a predetermined clamp voltage
V.sub.11 (V.sub.11=+Vcc+V.sub.F) by the diode D.sub.2 for clamping
at the time t.sub.ON when the lamp lighting switch is turned on, as
shown in FIG. 11. After that, the resistance value of the discharge
lamp is lowered and the output voltage V.sub.2 from the down
converter 8 of FIG. 7 is lowered. Therefore, as shown in FIG. 11, a
divided voltage V.sub.15 from the voltage-division resistors
R.sub.31, R.sub.32 is supplied as the ultimate detected voltage
V.sub.6 to the multiplier 42 and the power setting switching
circuit 62. This divided voltage V.sub.15 is expressed as
follows.
V.sub.15=V.sub.2.times.(R.sub.32/(R.sub.31+R.sub.32))
[0104] For example, this is approximately 10 V.
[0105] Next, the output voltage V.sub.5 from the power setting
control circuit 60 (V.sub.0 of FIG. 5) is an output obtained by
integrating the output V.sub.i from the lamp ON detection circuit
23 at the time-constant circuits of the resistor R.sub.9, capacitor
C.sub.2 and resistors R.sub.7, R.sub.8, and therefore it has a
voltage waveform such that the voltage continuously increases to a
voltage V.sub.21 with a predetermined time constant from the time
t.sub.ON when the lamp lighting switch is turned on, as shown in
FIG. 11. This voltage V.sub.21 is a voltage
(+Vcc.times.R.sub.7/(R.sub.7+R.sub.8)+V.sub.F) obtained by adding a
divided voltage (+Vcc.times.R.sub.7/(R.sub.7+R.sub.8)) of the
power-supply voltage +Vcc divided at the resistors R.sub.7,
R.sub.8, to a forward voltage drop V.sub.F of the diode D.sub.4.
This is equivalent to "V.sub.k+V.sub.F" obtained by adding the
divided voltage V.sub.k
(V.sub.k=V.sub.B.times.R.sub.2/(R.sub.1+R.sub.2)) of the
power-supply voltage V.sub.B divided at the resistors R.sub.1,
R.sub.2 to the forward voltage drop V.sub.F of the diode D.sub.1,
as described above with reference to FIG. 5.
[0106] As the output voltage V.sub.5 of the power setting control
circuit 60 is sent to the power setting circuit 61 and control
target power is set, the output power from the down converter 8 of
FIG. 7 is controlled so that the output (detected voltage) from the
multiplier 42 becomes this target power. That is, the control
target power in the power setting circuit 61 is set in accordance
with the output voltage V.sub.5 from the power setting control
circuit 60.
[0107] Meanwhile, when lighting of the lamp (discharge lamp) is
started, after the lapse of the lamp voltage constant period
T.sub.A (for example, approximately 20 to 90 seconds) as described
above, the lamp voltage build-up period T.sub.B begins and the
output voltage from the down converter 8 of FIG. 7 rises.
Therefore, the voltage V.sub.6 at the connection point between the
voltage-division resistors R.sub.3, R.sub.32 rises as shown in FIG.
11 and is supplied to the power setting switching circuit 62. The
power setting switching circuit 62 compares this voltage V.sub.6
with a predetermined threshold voltage V.sub.16 and the result of
comparison is reversed at time t.sub.13. As this result of
comparison is sent as a power setting switching output to the power
setting circuit 61, the preset target power of the power setting
circuit 61 is switched. For example, as the target power of the
output power from the down converter 8 of FIG. 7, target power of
30 W at the start-up before the time t.sub.13 is switched to
steady-state target power of 140 W after the time t.sub.13.
However, the present invention is not limited to these numerical
values.
[0108] According to the specific example described with reference
to FIGS. 10 and 11, similar to the embodiment described with
reference to FIGS. 1 to 5, the time during which a large current
larger than the steady-state current flows through the discharge
lamp can be reduced, and heat load on the electrodes and hence
thermal fatigue of the electrodes can be reduced. Therefore,
exhaustion of the electrodes can be restrained to the minimum level
and shortening of the lifetime of the discharge lamp due to the
exhaustion of the electrodes can be prevented.
[0109] A projector device as an embodiment of the present invention
constituted by using the discharge lamp lighting device of the
above-described embodiment of the present invention will now be
described with reference to FIG. 12.
[0110] FIG. 12 is a block diagram showing the schematic structure
of the projector device using the above-described discharge lamp
lighting device. This projector device shown in FIG. 12 has a lamp
(discharge lamp) 101 driven for lighting by the above-described
discharge lamp lighting device so as to emit light, an integrator
121 for uniformly illuminating an object with the light emitted
from the lamp 101, a condensing lens 122 for condensing, in
parallel, main light beams emitted from the integrator 121 and
directed toward respective spots on the object, a light bulb (123
to 125), which is an object to be illuminated with the light
emitted from the condensing lens 122 and modulates and outputs the
light incident thereon on the basis of an inputted image signal,
and a projection lens 126 for projecting image light outputted from
the light bulbs to a screen 127.
[0111] The integrator 121 is constituted by, for example, a
multi-lens array or the like having element lenses vertically and
horizontally arranged in the form of matrix. The element lenses at
the corresponding spots illuminate the whole light bulb by using
the light having intensity distribution emitted from the lamp 101,
thus causing the light incident on the light bulb to be
uniform.
[0112] In this embodiment, the light bulb is constituted by a
incident-side polarizing plate 123, a liquid crystal panel 124, and
an emitting-side polarizing plate 125. With respect to light in a
predetermined direction of polarization passed through the
incident-side polarizing plate 123, the liquid crystal panel 124
rotates the direction of polarization by a voltage applied thereto
on the basis of an image signal. A polarized light component in a
predetermined direction, of the light with the rotated direction of
polarization, passes through the emitting-side polarizing plate
125. Thus, an output (emitting light) modulated from the incident
light on the basis of the image signal is generated.
[0113] To equalize the direction of polarization of the light
incident on the incident-side polarizing plate 123, a PS converter
for converting light emitted from the lamp to light in a
substantially predetermined direction of polarization may be
provided near the integrator 121. Although one light bulb is used
in this embodiment as shown in FIG. 12, the projector device may
also be constituted by using three light bulbs corresponding to
primary colors, together with color separation means made up of a
dichroic mirror or the like and color synthesis means made up of a
dichroic prism or the like.
[0114] After an image signal inputted to an input terminal 116, for
example, a video signal, is decoded to a primary color signal of
RGB, the modulation at the liquid crystal panel 124 is carried out
by using a known structure including image signal processing means
117 for carrying out processing such as number-of-pixel conversion
in accordance with the element array of the liquid crystal panel
124 and a driver 118 for driving to apply a voltage to each pixel
of the liquid crystal panel 124 by an output from the image signal
processing means 117.
[0115] In the above-described structure, light emitted by lighting
the lamp 101 is made uniform by the integrator 121 and the
directions of main light beams of the light (luminous flux)
directed toward the respective spots on the liquid crystal panel
124 are made substantially parallel by the condensing lens 122. The
parallel light beams pass through the incident-side polarizing
plate 123 and become incident on the liquid crystal panel 124. By
the projection lens 126, which projects the image on the liquid
crystal panel 124 onto the screen 127, the light passed through the
emitting-side polarizing plate 125 is projected onto the screen
127. Thus, the projector device displays the image based on the
input image signal onto the screen 127.
[0116] Next, a starting system of the projector device in which the
lamp 101 is lit to emit light will be described. This starting
system substantially corresponds to the discharge lamp lighting
device described above with reference to FIGS. 1 and 7.
Hereinafter, it will be described on the basis of the structure
shown in FIG. 12.
[0117] In FIG. 12, the starting system has the above-described
discharge lamp lighting device which operates by using a DC power
source 109 for supplying power converted to a DC voltage from an
external AC power source 110. The lamp 101, an ignitor 102, a
voltage detection circuit 103, a current detection circuit 104, a
down converter 108, and the DC power source 109 are equivalent to
the discharge lamp 1, the ignitor 2, the voltage detection circuit
3, the current detection circuit 104, the down converter 8, and the
DC power source 9 of FIGS. 1 and 7, respectively. A power control
circuit 106 and a PWM controller 107 of FIG. 12 correspond to the
control circuit 6 and the PWM controller 7 of FIG. 1, or the
multiplier 42, the power setting circuit 61 and the control circuit
70 and the like of FIG. 7. Moreover, the starting system of FIG. 12
has a CPU 113 as a system microcomputer for controlling the whole
system of the projector device, a power switch 112 for giving an ON
command (or OFF command) to the CPU 113 on the basis of a user's
operation, and a standby power source 111.
[0118] In this starting system, the CPU 113 is adapted for
controlling the whole system and particularly functions as starting
control means for controlling the operations of the DC power source
109, the PWM controller 107 and the ignitor 102. Specifically, in
accordance with a system control program read from a ROM, not
shown, the CPU 113 receives an ON command from the power switch 112
and outputs a predetermined control command to a control object.
The CPU 113 also has a timer function to control the timing for a
control command.
[0119] The DC power source 109 is controlled to start (or stop)
power supply to the down converter 108, by a command S1 from the
CPU 113. Specifically, a semiconductor switch provided on the
output side from the active filter to the down converter 108 is
ON/OFF-controlled by the command S1.
[0120] The PWM controller 107 of the discharge lamp lighting device
is controlled to start (or stop) supplying a pulse to the down
converter 108, by a command S2 from the CPU 113. Specifically, a
rectangular wave with a predetermined duty factor is provided by a
comparator which compares a triangular wave generated by an
internal oscillator with a predetermined DC level and generates a
fan-out, the oscillation output of the triangular wave is
ON/OFF-controlled by the command S2. A lighting command S3 to the
ignitor 102 is to instruct start of the above-described discharge
lamp lighting operation.
[0121] In the above-described structure, in a so-called standby
state where the projector device is inoperative and the minimum
necessary function for starting operation is active by using the
standby power source, as the user turns on the power switch 112, an
ON command SO is given to the CPU 113. On the basis of this ON
command SO, the CPU 113 first outputs the command S1 to turn on the
DC power source 109 and the DC power source 109 starts supplying
power to the down converter 108. Meanwhile, the CPU 113 times the
time from the reception of the ON command S0 by using the timer,
and after a predetermined time, for example, 2 to 3 seconds, the
CPU 113 outputs the command S2 to turn on the output of the PWM
controller 107, so that a rectangular wave for the down converter
108 to start its function is supplied. After the preparation for
power supply to the lamp 101 is thus completed, the CPU 113 outputs
the lighting command S3 to the ignitor 102 to start lighting the
lamp 101. Thus, the lighting operation as described in the
above-described embodiment is started in the projector device.
[0122] In this manner, power supply from the DC power source 109 is
started, and when its output is stabilized after a predetermined
time, for example, 2 to 3 seconds, a rectangular wave for causing
the down converter 108 to function is supplied from the PWM
controller 107. Therefore, the down converter 108 can be securely
activated. Moreover, after the down converter 108 starts operation
and power is supplied to the lamp 101, the ignitor 102 carries out
the operation to light the lamp 101. Therefore, the lighting device
can operate while securely preventing the influence of a
transitional instability at the start of power supply.
[0123] After the lighting operation of the discharge lamp lighting
device is started, the current supplied to the lamp 101 after
ignition is controlled to gradually increase, as described in the
embodiments of FIGS. 1 and 7. Thus, the time during which a large
current larger than the steady-state current flows through the
discharge lamp can be significantly reduced, and heat load on the
electrodes and hence thermal fatigue of the electrodes can be
reduced. Therefore, exhaustion of the electrodes can be restrained
to the minimum level. Thus, in this projector device, shortening of
the lifetime of the lamp 101 due to the exhaustion of the
electrodes can be prevented. The current control means of the
discharge lamp lighting device can be realized with a simple
structure, and the discharge lamp lighting device with high
reliability can be produced inexpensively.
[0124] It is to be noted that the present invention is not limited
to the foregoing description and various changes and modification
can be made without departing from the scope of the present
invention.
* * * * *